During manufacture of semiconductor integrated circuits, a wafer-slice storage and conveyor apparatus is used by means of which a number of wafer slices to be in stock are stored in column form. Such a storage and conveyor apparatus includes a hollow, generally box-shaped storage unit having inner wall portions formed with a number of C-shaped grooves which are vertically arranged at regular intervals. Wafer slices are stored in the storage unit each with a portion of its peripheral edge received in each of the C-shaped grooves and can be delivered from the storage unit one by one by means of a transfer assembly which typically consists of a belt and pulley conveyor arrangement. The wafer slices are carried over by the transfer assembly to any process stage of the production line for the fabrication of semiconductor integrated circuits and may be returned to the storage unit also by means of the transfer assembly upon completion of the process steps at the stage.
Such a known storage and conveyor apparatus has a problem in that only the lowermost one of the wafer slices forming the columnar assembly within the storage unit is allowed to be passed to the transfer assembly during each delivery operation from the storage unit. The prior-art storage and conveyor apparatus further has a problem that none of the wafer slices which have been delivered from the storage unit can be returned to their respective original positions in the storage unit until the wafer slices which were taken out precedingly have been returned to the storage unit. These problems provide various restrictions on the steps of operation to be performed for the fabrication of integrated circuits using the wafer slices stored in the apparatus. Still another problem-inherent in a prior-art storage and conveyor apparatus of the described general nature is that the wafer slices stored therein are received along their peripheral edges in the grooves in the storage unit and may therefore receive scratches on the lower surfaces of the edge portions thereof when the slices are being withdrawn out of the storage unit.
It is, accordingly, an important object of the present invention to provide an improved storage and conveyor apparatus which will provide an increased degree of flexibility in the operation for the fabrication of semiconductor integrated circuits and which will thus permit significant reduction in the production costs of the integrated circuits.
It is another important object of the present invention to provide an improved storage and conveyor apparatus by means of which any desired wafer slice can be selected and transferred to a process stage from among the number of wafer slices stored in a storage unit without respect to the order in which the individual wafer slices are arranged in the storage unit.
It is still another important object of the present invention to provide an improved storage and conveyor apparatus in which the wafer slice which has once been taken out of the storage unit and used at the process stage can be returned to its initial position in the storage unit also without respect to the order in which the individual wafer slices are arranged in the storage unit.
It is thus still another important object of the present invention to provide an improved storage and conveyor apparatus which requires no extra storage unit additional to the storage unit currently in use.
It is, yet, still another important object of the present invention to provide an improved storage and conveyor apparatus in which a wafer slice is protected from being subjected to sliding friction that would otherwise produce scratches on the surface of the wafer slice while the slice is being withdrawn from the storage unit.